This application is a national stage application of International Application No. PCT/SE98/01437, filed on Aug. 5, 1998.
The present invention relates to a device for cleaning air from electrically charged particles (aerosols), said device including at least one precipitator panel, said panel including at least one precipitator unit having at least two electrode elements or at least two groups of electrode elements, said elements being located alternately relative to each other by a an internal gap distance, said electrode elements being suitably connected to respective terminals of a high voltage source, said device being located in an air flow duct or in immediate connection with an air flow duct.
Particle filters for use in ventilating applications or so called duct filters are usually designed around mechanical so called barrier filters. The separating capacity with regard to particle separation varies widely for these filters depending on the structural design (the filter class), i.e. coarse filters, fine filters and micro filters. Characterising for these filters are among other things an substantially increasing pressure drop in relation to the ability to separate micro particles. This disadvantage gives rise to a need for powerful air transporting fans, said fans having a high noise level and of course unnecessary high energy consumption together with expensive installation costs. Also, the increasing demands for improved indoor air and demands for clean ventilating ducts have increased the use of higher filter classes.
Mechanical filters of electrically charged fibres, so called electret filters, have initially better operation characteristics than other types of barrier filters. However, these characteristics are not operationally stable and decrease eventually.
The use of the traditional electro filter technique, i.e. using precipitators of metallic electrode elements instead of mechanical filters has up to now not been successful to any higher degree. This depends on high installation costs and complicated and expensive service. The recent development of the electro filter technique using filter cassettes of paper has up to now not been used in ventilating duct applications since also this technique has its limitations, especially in such a demanding environment as ventilating ducts, said environment having a temperature and a humidity that varies widely and an air flow velocity that is several times higher than in air cleaners, said air cleaners being the devices that the technique in question basically is developed for.
The reasons for said limitations are the following. The precipitator designed out of board (cellulose based material), i.e. high ohmic material, is affected by dust that bridges the gap between adjacent electrode elements, i.e. electrode elements connected to respective terminal of a high voltage source. This affection increases by increasing air humidity and decreases dramatically the particle separating capacity of electro filters. The bridging dust between adjacent electrode elements deflects namely the electrical charging from the surfaces of the electrode elements, the effect of this is that the potential between said surfaces decreases and consequently that the particle (aerosols) separation capacity decreases.
The aim of the present invention is to eliminate said limitations and thus create a practical and economical alternative for a new type of ventilating filter or duct filter of electrostatic character. In this connection the expression duct filter defines, apart from filters for domestic ventilation, i.e. filters for supply air and/or exhaust air, also other applications, e.g. filters for coupes of motor cars, i.e. integrated in the ventilating device of the motor car, and also other industrial applications having relatively high air flow velocities. It is of course also possible to use the technique in other circumstances, e.g. when designing air cleaners, cooker hoods etc. The most important advantages with the new type of filter are the high separating capacity of micro particles also in combination with simultaneous separation of heavier particles, this being effected by an extremely low pressure drop and simple service using a vacuum cleaner or replacement of the filter.